In recent years, a decrease in feature size of LSI patterns progresses. For example, in the field of DRAMs, a device integrating program is set forward for 256-M, 1-G, and 4-G DRAMs even after 64-M DRAMs are developed. In this situation, the exposure technique is regarded as a very significant technique in the micropatterning techniques. Particularly, the electron beam drawing technique is expected to be one of future promising exposure means as it can micropattern with a very small size of 0.1 μm or less.
A conventional electron beam drawing apparatus is a single-beam drawing scheme such as Gaussian beam scheme or variable shaped beam scheme. As this drawing scheme has a low productivity, it has been used in mask drawing, studies and development for VLSIs, and application fields for ASIC devices in small-amount production.
Recently, studies and development for the electron beam technique have progressed. From the viewpoint of productivity, a new multibeam drawing scheme which uses a plurality of electron beams to increase the drawing speed is proposed as a scheme that can be applied to the production of memory devices such as DRAMS, and is under further studies. With the multibeam drawing scheme, to obtain a throughput of 20 or more wafers/hour which is required in the production of semiconductor devices, several hundred beams or more are required. In view of this, a method of forming a multibeam by dividing one electron beam generated from one electron gun into a plurality of beams with a single electron beam column, a method of forming a plurality of beams with a multicolumn, and furthermore a method of forming a multibeam from beams of a multicolumn are proposed.
FIG. 4 shows an arrangement of a conventional typical Gaussian-scheme electron beam drawing apparatus. An electron beam drawing apparatus 1 of FIG. 4 is formed of an electron gun 2 using a three-pole-structure hot cathode, an alignment electrode 3, lenses 4 and 5, a deflector 6, a detector 7, and a stage 9 for placing a wafer 8.
FIG. 5 is a view showing a multicolumn electron beam drawing apparatus having a plurality of columns each formed of an electron gun and lens system. With the multicolumn scheme electron beam drawing apparatus having a plurality of electron guns in this manner, a high throughput can be obtained.
With the multielectron gun 2 having the multiple columns of three-pole-structure electron guns as shown in FIG. 5, to have the uniform (same) characteristics of the electron guns, e.g., brightness, beam current, crossover diameter, and angular current distribution, among the plurality of electron guns 2 (2a, 2b, and 2c), the temperatures of cathodes 21 (21a, 21b, and 21c) and the bias voltages of Wehnelt electrodes 22 (22a, 22b, and 22c) must be adjusted separately for the respective electron guns.
According to the conventional single column scheme shown in FIG. 4, the temperatures and biases as described above can be adjusted by considering only the characteristics of the electron source and Wehnelt electrode of one electron gun 2. In contrast to this, in the multielectron gun 2 shown in FIG. 5, the temperatures and biases must be adjusted separately by considering the characteristics of the electron sources and Wehnelt electrodes of the respective electron guns 2 (2a, 2b, and 2c). The characteristics of the respective electron guns, however, are difficult to set uniformly particularly because of slight differences in the shapes and surface states of the electron sources and in the shapes of the Wehnelt electrodes. Accordingly, the temperature conditions of the respective electron guns and the bias conditions of the Wehnelt electrodes must be set at different values. When the electron gun is used over a long period of time, as the cathodes wear or deform, the electron beam emitting characteristics change. Thus, the temperatures of the cathodes and the voltages of the Wehnelt electrodes must be adjusted constantly.
In this manner, in the multielectron gun having a plurality of columns of three-pole-structure electron guns, the same voltage cannot always be applied to the Wehnelt electrodes of all the electron guns. Then, field interference occurs between the columns of adjacent electron guns (between the Wehnelt electrode and anode electrode of one column and between the Wehnelt electrode and anode electrode of the adjacent column), and the uniform characteristics cannot be maintained in all the electron guns. Furthermore, when the bias voltage changes during drawing, the beam current and emission distribution characteristics of the electron beam and the shape and position (trajectory) of the crossover image fluctuate because they are adversely affected by an adjacent beam. Therefore, it is difficult to obtain a stable, highly uniform multielectron gun. Accordingly, it is also difficult to obtain an electron beam exposure apparatus in which the plurality of beams have uniform characteristics.